Paintballs for use in paintball guns (also referred to as markers) are constructed from fragile materials that are designed to break on contact with a target.
Paintballs are fired from a marker by gas pressure acting as a propellant and therefore in the construction of a paintball a balance needs to be struck between ensuring that the paintball is strong enough to withstand the initial propellant gas pressure but fragile enough to fracture upon impact. It is therefore desirable to apply as little force as possible to the paintball from the gas pressure, while still imparting sufficient kinetic energy to the paintball. This has lead to the development of lower pressure paintball markers which in turn has also allowed the evolution of more fragile paintballs which, due to their increased fragility, disperse their kinetic energy better upon impact.
Some problems with this low pressure operation are that losses can become greater and the airflow becomes more critical as the speed of operation of the gas delivery system is still required to be fast but needs to achieve higher gas flows at lower pressures.
In blow back type paintball guns, a hammer is moved by a spring when the trigger is pulled and opens a valve to release the gas pressure which fires the paintball. The gas pressure which is used to fire the paintball is also used to push (or ‘blow’) the hammer back against the force of the spring to re-cock the gun.